igneous

Obsidian

Volcanic Glass (Silicon Dioxide with impurities)

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark brown/green, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Hardness: 5-5

Identified February 6, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark brown/green, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents the growth of crystals. It is typically found in quaternary volcanic regions associated with subduction zones or hotspots.

Uses & applications

Used historically for arrowheads and knives; currently used for surgical scalpel blades, ornamental jewelry like beads and cabochons, and as a collector's specimen.

Geological facts

Because it is glass, obsidian breaks with a conchoidal fracture, creating edges that are thinner and sharper than high-quality steel surgical scalpels. It is technically a mineraloid rather than a mineral because it lacks a crystal structure.

Field identification & locations

Identify in the field by its distinct glassy appearance, smooth curved (conchoidal) fracture lines, and sharp edges. Common in volcanic areas like Iceland, Mexico, and the Western USA (Oregon, California). Collectors look for variations like 'Snowflake' or 'Mahogany' obsidian.

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Fluorapatite (Ca5(PO4)3F)

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Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Magnetite

Magnetite (Fe3O4)

mineral